1. Field of the invention
The present invention relates to a method and apparatus for cleaning a surface material from an underlying surface of a substrate, and more particularly to such a method and apparatus where the underlying surface is susceptible to damage by impingement of high pressure water jets. A particular application of this is for the removal of rubber or paint from an airport runway surface made of concrete or asphalt/rock aggregate material.
2. Background Art
When airplanes land on a runway, the tires of the airplane will commonly skid over the runway surface for a certain distance, with some of the rubber from the tires becoming deposited on the runway surface and also being bonded thereto. Over a certain period of time, this layer of rubber can accumulate so as to become a safety hazard. Accordingly, it has been found to be desirable to remove this rubber layer at periodic intervals.
One method of removal of surface material is by use of high pressure water jets, and this method is sometimes used in cleaning runway surfaces. The commercially practiced prior art method known to the applicants herein is one where water jets at a pressure of approximately 10,000 psi are arranged in an array at a stationary location on a vehicle, and the vehicle moves over the runway surface at a speed of up to possibly as high as ten miles per hour. However, it has been found rubber removal from the runway in this manner is less than totally effective. There is a further problem that the runway itself is damaged by having runway surface material flake off.
This damage is particularly noticeable where there is a grooved concrete runway. To explain this more fully, it sometimes happens that over a period of time the concrete surface becomes smooth due to repeated aircraft landings, and grooves of possibly 3/8th of an inch depth and 3/8th of an inch spacing are cut along the runway transverse to the direction of landing of the airplanes, this being done to improve traction between the airplane tires and the runway. However, rubber will eventually fill these grooves, and also become deposited on the total runway surface. When it is attempted to remove this rubber by means of the prior art water jet method as described above, these ridges that define the grooves in the concrete are particularly susceptible to damage from the water jets.
A search of the patent literature has disclosed a number of patents which deal with this general problem area. The following patents are directed specifically toward the problem of cleaning the rubber from airplane tires from runway surfaces.
U.S. Pat. No. 3,877,643 (Smith et al) shows an apparatus for removing a rubber coating from airport runways where a plurality of water jets are discharged from a manifold that is mounted to a vehicle. The manifold is reciprocated laterally transverse to the direction of travel of the vehicle a distance at least equal to the longitudinal distance between adjacent nozzles. In column 3, last line, it is indicated that the pressure of the water at the nozzle should be within a range of four thousand to eight thousand P.S.I.
U.S. Pat. No. 3,848,804 (Prestwich) discloses a machine for removing rubber from runway surfaces where a sheet of water, preferably hot water, is emitted from nozzles. It is stated that the pressure should be as high as possible without causing damage to the surface and at least as high as fifty P.S.I. These nozzles are moved in a arcuate path.
U.S. Pat. No. 3,726,481 (Foster) discloses a machine for directing high velocity water jets from a manifold against a runway surface to remove rubber. At the top of column 7, it is stated that the water is discharged as jets at four thousand pounds per square inch.
U.S. Pat. No. 3,709,436 (Foster) shows another runway cleaning machine where there is a frame which carries a manifold and which is adapted to be removably mounted on the front of a forklift. Fan-shaped jets are utilized. No operating pressures are specified.
U.S. Pat. No. 3,987,964 (Pittman et al) discloses a machine adapted to clean rubber and the like from a runway, where there is provided a plurality of fan-shaped water jets which are emitted from a stationary manifold mounted on the front part of a truck. In column 7, line 46, it is stated that the pressure of the water is in the range of two hundred to twenty thousand pounds per square inch, with a preferred pressure of around six thousand pounds per square inch. The truck to which the jet manifold is mounted travels at a linear velocity as high as about ten miles an hour and preferably around two to four miles per hour, depending upon the amount of contaminates deposited on the surface and to what degree these stick to the surface.
British Patent Specification 1,327,799 (Prestwich) shows a runway cleaning apparatus where nozzles are positioned at the ends of a rotating arm, with water of at least fifty P.S.I. being emitted from these nozzles to impinge upon the runway surface.
The following five patents are directed toward providing high pressure water jets, but it is not clear whether these patents show any features directed specifically toward the cleaning of airport runway surfaces or the like.
U.S. Pat. No. 4,600,149 (Waktsuki) discloses an apparatus for producing water jets at a pressure of two thousand kilograms per square centimeter. The nozzles which discharge the jets are mounted in a rotating structure so that these jets move in a generally circular path.
The following four patents relate generally to specifics of the construction of the nozzle or the mounting thereof, these being the following:
U.S. Pat. No. 3,902,670 (Koller et al);
U.S. Pat. No. 4,244,524 (Wellings);
U.S. Pat. No. 4,728,041 (Traxier); and
U.S. Pat. No. 4,802,628 (Dautel et al)